Evaporator

ABSTRACT

The present invention is a cross-flow evaporator adapted to generate vapor from the heat of the exhaust gases from an internal combustion engine. The evaporator is constituted, among other elements, by two plates spaced from one another which contain chambers. The heat exchange tubes alternately communicate the chambers of both plates, establishing a specific path for the fluid intended to change phase. The tubes extending between the chambers of the two plates are arranged transverse to the flow of the hot gas. This evaporator is suitable for heat recovery systems using a Rankine cycle, making use of the heat from the exhaust gases. 
     The invention is characterized by a special configuration of the walls which prevents the crack failure or damage caused as a result of the differential expansion between the exchange tubes and said walls.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is filed under 35 U.S.C. §119(a) and claims priority toEuropean Patent Application No. EP15382533.6, filed Oct. 28, 2015 andentitled “Evaporator” in the name of Adrián FOLGUEIRA BALTAR,incorporated herein by reference in its entirety.

OBJECT OF THE INVENTION

The present invention relates to a cross flow evaporator adapted togenerate vapor from the heat of the exhaust gases from an internalcombustion engine. The evaporator is constituted, among other elements,by two plates spaced from one another which contain chambers. The heatexchange tubes alternately communicate the chambers of both plates,establishing a specific path for the fluid intended to change phases.The tubes extending between the chambers of the two plates are arrangedtransverse to the flow of the hot gas.

This evaporator is adapted for heat recovery systems using a Rankinecycle, making use of the heat from the exhaust gases.

The invention is characterized by a special configuration of the wallswhich prevents the crack failure or damage caused as a result of thedifferential expansion between the exchange tubes and said walls.

BACKGROUND OF THE INVENTION

Heat exchangers are devices intended for transferring heat from a firsthot fluid to a second fluid which is initially at a lower temperature.

A specific case of heat exchangers is those exchangers intended forcooling the hot exhaust gas for EGR (Exhaust Gas Recirculation) systemsthrough a liquid coolant. This type of heat exchangers must overcomespecific technical problems due to temperature changes in theirdifferent components.

The temperature variation ranges go from its resting state, where allthe components are at room temperature, to its operative mode, where theinlet gases may reach more than 600 degrees centigrade, producingsignificant differences in temperature in different parts of the device.

The structure of this type of exchangers is configured as a heatexchange tube bundle through which the hot gas circulates, and this tubebundle is housed in a shell through which the liquid coolant circulates.

If the liquid coolant enters and exits approximately at points of theshell located near the ends of the tube bundle, then the flows of gasand liquid circulate approximately according to parallel directions,whether co-current or counter-current.

Problems caused by thermal expansion are solved by making use ofintermediate manifolds, which receive or deliver the hot gas, which inturn have bellows-type structures that compensate for the differentialexpansion between the tube bundle, in contact with the hot gas, and theshell, in contact with the liquid coolant.

A different type of heat exchanger is that consisting of evaporators.Evaporators are heat exchangers designed to transfer the heat of a hotgas to a liquid that is not only heated up but also changes phase.

The technical challenges presented in an evaporator are greater thanthose of a heat exchanger such as the one described at the beginning ofthis section. The phase change allows differentiating three steps inconnection with the temperature and the state of the liquid changingphase:

-   -   i. step of heating the liquid to be evaporated;    -   ii. step of changing phase;    -   iii. step of overheating.

The first and second steps occur at not very high temperatures, sincethe phase change temperature establishes a barrier which preventsraising the temperature above the evaporation temperature. In contrast,the overheating step is not limited by the phase change and may raisethe temperature up to values close to maximum temperature values for thehot gases.

The inlet temperature conditions of the two fluids, the hot gas thattransfers its heat and the liquid intended for changing phase, are notalways the same and neither are the inlet flow rates. The variation ofthese variables means that the interphase between the first and secondstep, and the interphase between the second and third step, do not occurin the same place inside the evaporator, in connection with the path ofthe liquid intended for changing phase inside the device, rather it canoccur in different places within a certain interval of said path.

Additionally, going from liquid to vapor and going from the mixture ofliquid and vapor to superheated vapor is not instantaneous, so noprecise place may be identified where the division is establishedbetween steps, rather such divisions are in a specific segment.

Each of the steps has different heat exchange conditions. The heattransfer coefficients between the surface of the heat exchange tube andthe liquid (step i) are very different from those of a two-phase flow,i.e., the flow formed by liquid plus vapor (step ii), and very differentfrom the heat transfer coefficients of the superheated vapor (step iii).

Not only are the heat transfer coefficients different, but the specificvolume in the liquid is very low with respect to the specific volume inthe liquid-plus-vapor mixture, and this in turn is low with respect tothe specific volume of vapor when the temperature thereof is rising.

All these very different factors between the three steps make the designvariables different and the evaporator have technical difficulties thata heat exchanger with no phase change does not present, above all whenthe evaporator must be compact and occupy the smallest possible space.

Compact heat exchangers are known that are designed to act asevaporators in heat recovery systems in internal combustion engines forimpulsion of vehicles. These evaporators increase the heat exchangesurface by arranging a bundle of pairs of coaxial tubes. The liquidintended for changing phase passes through the space between the pair ofcoaxial tubes and the hot gas passes both inside the inner tube andoutside the outer tube.

The fluid changing phase passes between two hot surfaces with littledistance between them so that the raising of the temperature and thesubsequent phase change takes place within a length of the pair ofcoaxial tubes that is shorter than if only one tube for circulating thefluid changing phase therein and the hot gas on the outside thereof,were used.

With this configuration one of the problems that exists is that thethree heat exchange steps take place throughout the same tubes, so thedesign of the exchanger cannot be optimized for the three steps at thesame time.

As an example of this difficulty, the speed of the inlet flow in liquidphase may be very low due to the low value of the specific volume, whileat the outlet, the same liquid flow rate corresponds to a much largervolume of vapor, which imposes much higher speed values than those ofthe entrance of liquid.

Low speed at the inlet can lead to the deposition of dirt and the highspeed of the vapor at the outlet can generate excessive pressure drops.

The present invention avoids these problems by using a cross-flowconfiguration between the hot gas and the fluid changing phase.

The evaporator is constituted, among other elements, by two platesspaced from one another which contain chambers. The heat exchange tubesalternately communicate the chambers of both plates.

The hot gas flows between the plates, parallel to both, in a volumeclosed by side walls. With this configuration, the exchange tubes aretransverse to the flow. The length needed to obtain the vapor at aspecific temperature is attained by incorporating the number of tubesneeded to reach the length which allows the sufficient heat transfer andtherefore cover the three steps.

An advantage that this configuration has is the possibility ofcommunicating two chambers with more than one heat exchange tube in sucha way that, after a phase change takes place, the chambers between whichthe fluid is being transferred can be communicated with a growing numberof tubes. The growing number of tubes is equivalent to an increase inthe passage section, and the device thereby takes into account theincrease in the specific volume with the phase change.

Expansion of a heat exchange tube depends on the thermal expansioncoefficient and on the total length of the tube. With the configurationof the device according to the invention, each of the individual tubesextending between both plates is much shorter than the total length ofthe path, so the effect of expansion is noticeably reduced.

Nevertheless, although expansion of each of the tubes is noticeablyreduced, the tubes conveying the first fluid in the first step, in thesecond step and in the third step are at very different temperatures,their ends being attached to the same plates. The differential expansionbetween tubes means that along the path of the first fluid inside theevaporator, the plates tend to be spaced in an unequal manner betweenthe inlet of the first fluid and the inlet of the second fluid.

This differential expansion is furthermore restricted by the wallsenclosing the volume where the second fluid, i.e., the hot gas, passesbecause such walls are also attached to the plates connected at the endsof the exchange tubes.

The differential expansion between all these structural elementsgenerates stresses that can give rise to the crack failure of thedevice.

The present invention establishes a configuration that solves thisproblem. Additional solutions are established by means of embodimentswhich provide a device showing greater energy use and even lowerstresses due to the effect of thermal expansion.

DESCRIPTION OF THE INVENTION

As indicated at the end of the preceding section, a first aspect of theinvention is an evaporator for the evaporation of a first fluid by meansof the heat provided by a second fluid, the second fluid being a hotgas.

According to a preferred example, as will be described below, the fluidintended for changing phase is ethanol, an alcohol, and the hot gas isthe exhaust gas of an internal combustion engine. One very usefulapplication is the use of the evaporator in a Rankine cycle to recoverthe heat from the exhaust gases in the form of mechanical energy whichwould otherwise end up being discharged into the atmosphere.

The evaporator comprises:

-   a first plate and a second plate facing one another and arranged    spaced from one another, defining an inner face, the face facing the    other plate, and an outer face opposite the inner side; wherein each    of the plates comprises a plurality of chambers;-   an intake manifold of the first fluid and an exhaust manifold of the    first fluid located in fluid communication with one another and with    at least one different chamber of any of the plates;-   a plurality of heat exchange tubes wherein each of the heat exchange    tubes extends between a chamber of the first plate and a chamber of    the second plate; wherein each chamber of a plate is in fluid    communication with two or more chambers of the other plate by means    of at least two heat exchange tubes, except the chambers in fluid    communication with the intake manifold or the exhaust manifold;-   there being for each of the heat exchange tubes a path of fluid    communication from the intake manifold to the exhaust manifold    passing through the inside of said heat exchange tube;-   two side walls extending between the first plate and the second    plate housing the plurality of heat exchange tubes and establishing    between both a space for the passage of the second fluid, wherein    the second fluid enters through an inlet and exits through an    outlet;

The flow of the second fluid, the hot gas, is established between aninlet and an outlet throughout a space defined by the two plates and bythe two side walls. In the preferred configuration the two plates areparallel to one another and the side walls are also parallel to oneanother and perpendicular to the two plates. A prism with rectangularbases is defined with this configuration.

The heat exchange tubes extend between the chambers of both plates,crossing the inner space defined by the plates and the walls. Thearrangement of the exchange tubes with respect to the main flow of thesecond fluid is transverse.

The exchange tubes alternately transfer the flow of the first fluid fromone chamber of the first plate to another chamber of the second plate. Afirst chamber is communicated with an intake manifold of the firstfluid.

The passage from one chamber located in the first plate to the chamberlocated in the second plate, or vice versa, is made through the exchangetubes. The exchange tubes are located crossing the flow of the secondfluid, i.e., the hot gas. It is in this passage through the exchangetubes where the second fluid transfers its heat to the first fluid.

The last chamber is communicated with an exhaust manifold that collectsthe first fluid in superheated vapor phase, and takes it to the conduitwhich leads it to the application for which it is intended.

When the first fluid enters it is in liquid phase with a reducedspecific volume. The necessary liquid flow rate can be transported bymeans of one or a few exchange tubes. Therefore, the first chambers ofboth plates are connected through one or a few heat exchange tubes.

Once the first step of raising the temperature of the liquid has passed,the phase change begins where the appearance of vapor increases thespecific volume. After a specific chamber, i.e., the chamber where thesecond step is expected to begin, the number of heat exchange tubescommunicating one chamber with the next chamber of the other plate ishigher, giving rise to an increase in the passage section whichcompensates for said increase in the specific volume, reducing the speedand pressure drop.

According to preferred examples of the invention, the consecutivearrangement of the chambers is ordered according to the direction ofmovement of the second fluid, i.e., the hot gas, where transverse pathscan also be drawn in a zigzag configuration, depending on the width ofthe evaporator. The set of exchange tubes is therefore arranged in avery compact and orderly manner, and said order does not preventincreasing the number of tubes per chamber.

With this configuration, the first fluid enters a first chamber throughthe intake manifold. From this first chamber it passes to anotherchamber of the opposite plate through one or more heat exchange tubes.This first fluid alternately passes from chambers of one plate tochambers of the other plate, being able to increase the number of heatexchange tubes communicating one chamber to another to compensate forthe increase in specific volume due to the phase change. Once the lastchamber is reached, this chamber is in fluidic communication with theexhaust manifold which discharges the first fluid in the form ofsuperheated vapor.

Additionally, in the evaporator the side walls are elasticallydeformable, allowing to compensate the differential expansion betweenthe heat exchange tubes and said side walls.

The walls of the evaporator are in contact with the second fluid, i.e.,the hot gas, whereas the heat exchange tubes are in contact with bothfluids, with the first fluid on the inner portion thereof and with thesecond fluid on the outer portion thereof. These two differentconditions give rise to expansions in the direction of the exchangetubes which are also different.

Given that the side walls and the exchange tubes are attached to thefirst and to the second plate, differential expansion causes stressesthat can give rise to structural damage or even the crack failure of theevaporator.

Not only is there differential expansion between the walls and theexchange tubes, but the expansion and the differences in expansionbetween these components changes at least along the forward movementdirection of the first fluid, the fluid that changes phase, becausedepending on the phase of such fluid, the temperatures of the tubes aredifferent and the variation thereof is not even linear along the paththereof.

All these causes are grounds for the crack failure of the evaporator, orat least for the generation of stresses causing damage to the welds, orthey are a cause of fatigue in the materials. The invention solves thisproblem incorporating elastically deformable side walls which yield tothe expansion imposed by the tube bundle, drastically reducing stressesdue to the differential expansions identified above.

The elastically deformable feature means that the material from whichthe part is made allows deformation in the event of a stress and that,after deformation, the part recovers its original shape when the causesgenerating said deformation cease. Nevertheless, in the scope of theinvention, the existence of minor plastic deformations, particularly inthermal fatigue conditions, is allowed.

In the strict sense, when plastic deformation occurs, such deformationis referred to as elastoplastic deformation. These minor plasticdeformations continue to favor solving the problem given that they alsoabsorb differential expansions between elements.

The term elastically deformable used throughout the description andclaims must be interpreted in this broader sense, where it is possiblethat a minor percentage of the deformation is plastic deformation.

The result is a reduction of maximum stresses attained in givenstructural parts of the evaporator, increasing the service life of saidevaporator as it is not subjected to the same degree of thermal fatigue.

Various additional technical solutions solving other specific problemswill be shown by means of the description of the embodiments.

DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the invention will be betterunderstood based on the following detailed description of a preferredembodiment, given solely by way of illustrative, non-limiting example inreference to the attached drawings.

FIG. 1 shows a perspective view of an embodiment of the invention. Inthis figure, some heat exchange tubes have been intentionally removedfrom the inside for greater clarity.

FIG. 2 shows a schematic section view of another embodiment of theinvention that allows observing the inside of the evaporator, of the twoplates and of some of the chambers, as well as the exchange tubes goingfrom one plate to the other.

FIG. 3A shows a detail of a schematic section of another embodiment thatallows observing a constructive detail of the plate, manufactured bymeans of stacking of die-cut plates, in which the chambers areconfigured.

FIG. 3B shows a top view of an embodiment of one of the die-cut metalsheets giving rise to one of the main plates of the evaporator.

FIG. 4 shows a perspective view of one of the plates according toanother embodiment, in which the chambers are configured.

FIG. 5 shows a cross section with respect to the longitudinal directionX-X′ defined by the direction of the flow of the second fluid of oneembodiment with first walls situated on the outside and second wallssituated on the inside.

FIG. 6 shows a perspective view of an embodiment of an elasticallydeformable wall.

DETAILED DESCRIPTION OF THE INVENTION

According to the first aspect of the invention, the present inventionrelates to an evaporator intended for transferring the heat from a hotgas to a liquid, which raises its temperature, changes phase and exitsas superheated vapor.

In the embodiments, the hot gas, the one identified as second fluid, isthe exhaust gas of an internal combustion engine. In these embodiments,the first fluid is ethanol. Ethanol enters in liquid phase inside theevaporator. The transfer of heat from the second fluid to the firstfluid leads to a first step where the temperature of the first fluidraises until reaching the boiling temperature; in a second step itchanges phase, maintaining the temperature about equal to the boilingtemperature; and in a third step, in the vapor phase the temperaturefurther increases.

In this embodiment, the superheated ethanol vapor is used in a Rankinecycle to generate mechanical energy recovering part of the heat from theexhaust gases of the internal combustion engine.

As shown in FIGS. 1 and 2, according to embodiments of the invention,the evaporator is formed by two rectangular plates (1, 2), with twolonger sides and two shorter sides, spaced from and parallel to oneanother. In the figures, the parallel plates (1, 2) are depicted asbeing horizontal up and down according to the orientation of thedrawings.

The longer sides of the plates (1, 2) are connected by means ofrespective side walls (6) in the form of a flat plate that limits aprismatic-shaped internal volume with essentially rectangular bases.These side walls (6) are the walls depicted as being vertical in FIG. 1.

The shorter sides of the plates correspond to the ends of the evaporatorwhere the inlet (I₂) for the second fluid is located, and the outlet(O₂) is located at the opposite end. The direction of the second fluidestablishes a longitudinal direction identified as X-X′ in FIG. 2.

Each of the plates (1, 2) has a plurality of chambers (1.1, 2.1).Exchange tubes (3) extend from one chamber (1.1, 2.1) of a plate (1, 2)to another chamber (1.1, 2.1) of the other plate (1, 2). The heatexchange tubes (3) are arranged transverse to the flow of the secondfluid; i.e., transverse to the longitudinal direction X-X′.

Each chamber (1.1, 2.1) has exchange tubes (3) such that it is in fluidcommunication with two or more chambers (1.1, 2.1) of the other plate(1, 2). The chamber receives the first fluid through the exchange tubes(3) coming from a chamber (1.1, 2.1) of the other plate (1, 2) and thefluid exits towards the other chamber of the other plate (1, 2) throughthe other exchange tubes (3) connecting them.

FIG. 2 schematically depicts this condition by offsetting the chambers(1.1) of the first plate (1) and the chambers (2.1) of the second plate(2) according to the longitudinal direction X-X′.

By means of this connection of the chambers (1.1, 2.1), the first fluidpasses through the chambers sequentially, crossing from one plate (1, 2)to the other through the exchange tubes (3).

According to the section view depicted in FIG. 2, the flow of the firstfluid follows a zigzag path, alternating between the first plate (1) andthe second plate (2), moving from left to right. Nevertheless, there canbe additional chambers (1.1, 2.1) according to the transverse directionwhich are prolonged according to the direction perpendicular to theplane of the paper, as depicted in FIG. 2, such that the path can alsoalternate between the first plate (1) and the second plate (2),following a zigzag path, before passing to the next chamber (1.1, 2.1)according to the direction X-X′.

Another option that allows increasing the volume of flow that isconveyed is to use two or more rows of tubes in the communicationbetween two chambers.

The heat exchange tubes (3) are distributed inside the prismatic volumedefined by the plates (1, 2) and the side walls (6) with an orientationtransverse to the direction of the main flow of the second fluid. Thepath followed by the first fluid in the path, alternating between thefirst plate (1) and the second plate (2), will depend on how thechambers (1.1, 2.1) of both plates (1, 2) are overlapped, overlap beingunderstood as that obtained by means of a projection according to thedirection perpendicular to any of the mid-planes of the plates (1, 2).The chambers (1.1, 2.1) between which the passage of the first fluid inthe first plate (1) and in the second plate (2) is alternated are shownas being consecutively overlapped according to a projection in thedirection perpendicular to both plates (1, 2).

Said FIG. 2 shows a first chamber (1.1) of the first plate (1) in fluidcommunication with an intake manifold (4). The path of the first fluidends in a last chamber (2.1) of the second plate (2) in fluidcommunication with a second outlet manifold (5).

In the example shown in FIG. 1 the inlet manifold (4) and outletmanifold (5) are in the same plate (1), whereas in the example shown inFIG. 2 they are in different plates (1, 2).

In the embodiment of FIGS. 2 and 5, the plates (1, 2) have chambers(1.1, 2.1) configured by means of machining. The machining of thechambers (1.1, 2.1) gives rise to slots such as those shown in FIG. 4.In FIGS. 2 and 5, the heat exchange tubes (3) are depicted as beingparallel and in FIG. 4, the perforations that receive the exchange tubes(3) are offset, leaving a staggered distribution.

Each of the slots is closed with an upper metal sheet configuring eachof the chambers (1.1, 2.1) therein from the slots.

The detail of FIG. 3A shows an alternative way of configuring the mainplates (1, 2) of the evaporator. Each of the main plates (1, 2) is inturn formed by a first elemental plate (1.2, 2.2) having perforations toallow for the passage of the ends of the heat exchange tubes (3), and asecond elemental, die-cut plate (1.3, 2.3) with perforations toconfigure the chambers (1.1, 2.1), the first elemental plate (1.2, 2.2)and the second elemental plate (1.3, 2.3) being attached to one another.

In this particular example, to limit the thickness of the plate to bedie-cut, two identical die-cut plates are used, and once stacked formthe second elemental plate (1.3, 2.3). The desired thickness, or inother words, the height of the chamber (1.1, 2.1) formed by theperforations, can be obtained by stacking a plurality of plates (1.3,2.3).

FIG. 3B shows a second die-cut plate (1.3, 2.3) with the perforationsgiving rise to the chambers (1.1, 2.1).

In the described examples, whether the slots are formed by a machiningoperation on the plate (1, 2) or are obtained by stacking second die-cutplates (1.3, 2.3), the inner walls (1.1.1, 2.1.1) of the slots areperpendicular to the main plane of the plate (1, 2). Nevertheless, othermethods for producing a slot do not have to give rise to vertical walls.

FIG. 5 shows a section of the evaporator perpendicular to direction X-X′established by the flow of the second fluid and according to oneembodiment.

According to the section and according to the position shown in FIG. 5,the first plate (1) is arranged at the top and the second plate (2) isarranged at the bottom. The section coincides with chambers (1.1, 2.1)which, in both the upper plate (1) and lower plate (2), extend along theentire width.

If the section were to be established at a point closer to the inlet ofthe first fluid, this same section could present a larger number ofchambers (1.1, 2.1) such that there is also an exchange between bothplates (1, 2) according to a transverse path. This transverse path wouldbe contained in the plane corresponding to the section.

The heat exchange tubes (3) are subjected to the heat of the hot gas onthe outer surface thereof and to the first fluid, ethanol, with a lowertemperature, on the inner surface thereof. Particularly in the firststep, the temperature of the tubes is below the boiling temperature forethanol. At the end of the evaporator, the tubes are at temperaturesclose to the inlet temperature of the hot gas because the ethanol isoverheated. This temperature gradient gives rise to a progressiveexpansion from one end of the evaporator to the opposite end.

The plates (1, 2) are linked through both the heat exchange tubes (3)and the walls (6). According to the example shown in FIG. 1, the walls(6) are in contact with the hot gas.

The larger spacing between plates (1, 2) and the fact that this spacingis larger at one end than at the other generates stress in the walls(6). This stress can give rise to excessive values causing damage to, oreven the crack failure of, the evaporator.

The invention establishes as a condition that the walls (6) must beelastically deformable, such that the stress generated by the greaterdifference in thermal expansion with the exchange tubes is compensatedwith the elastic deformation of the walls (6). A particular way ofachieving the walls (6) to be elastically deformable is by using plateswith one or more crimps or corrugations (6.1) according to the directiontransverse to the direction in which they are desired to be elasticallydeformable.

A particular configuration of the crimps (6.1) is sinusoidal. Theadvantage of such crimps (6.1) is that the two main directions of theplane containing the plate in the path of the crimp along the sinusoidare combined, and greater stiffness against bending is maintained whileproviding the capacity of being elastically deformable with respect totension in the direction transverse to the main axis of the sinusoid.

In order to compensate for the progressive expansion of the heatexchange tubes (3) according to longitudinal direction X-X′ in which thehot gas flows, according to one embodiment the crimps (6.1) extendaccording to said longitudinal direction X-X′ whether they arelongitudinal or sinusoidal.

According to another embodiment, the heat exchange tubes (3) are alsoelastically deformable. One way of getting them to be elasticallydeformable is by means of a helical corrugation.

Compression of the heat exchange tubes (3) reduces the gap betweenplates as a result of expansion and further reduces stresses to agreater extent.

The expansion occurring on the walls (6) is caused primarily by the factthat they are in direct contact with the hot gas. According to theembodiment shown in FIG. 5, the evaporator comprises second walls (7),situated on the inside and spaced from the first walls (6). Now theseinner second walls (7) are the ones in direct contact with the hot gas.The second walls also extend between the first plate (1) and the secondplate (2). These second walls are elastically deformable such that theexpansion caused as a result of the hot gas is compensated for withtheir capacity for being elastically deformed.

In the graphical depiction, a corrugated line has been used to show thatit has a corrugated configuration (7.1), which is what provides saidsecond walls with their elastically deformable behavior.

In this embodiment elastically deformable first walls (6) andelastically deformable second walls (7) have been selected, where thestiffness of the first walls (6) is greater than the stiffness of thesecond walls (7). With this configuration, the inner walls demarcate theflow of the hot gas and do not increase stresses due to the more notableeffects of expansion, and the first walls (6) provide the necessarystiffness to the entire assembly without generating stresses thatgenerate fractures because they are also elastically deformable.

Between the first walls (6) and the second walls (7) there is a chamber(10) that can contain insulating means, preventing heat from seeping outreducing the heat recovery capacity of the device.

Air, a coolant, ethanol, or even vacuum are considered among theinsulating means.

According to another embodiment, when the first fluid, in this caseethanol, is in liquid phase it is made to pass through the chamber (10)formed between the first walls (6) and the second walls (7). This liquidcools both walls (6, 7), and in particular the second walls (7) whichare at a higher temperature as they are in direct contact with the hotgas.

As an additional effect, the temperature of the first fluid increases.The passage through the chamber (10) is carried out before introducingthe first fluid in the inlet into the manifold (4) communicating withthe first chamber (1.1) of the first plate (1). The first fluidtherefore has a temperature closer to the boiling temperature, and theenergy required for the first step as well as the total length of theheat exchanger are reduced.

According to the embodiment shown in FIGS. 2, 3A and 5, the evaporatorincludes two shield plates (11). The first plate (1) has a shield plate(11) spaced from said first plate (1) as shown on the top part of theevaporator, and the second plate (2) has a shield plate (11) also spacedfrom the second plate (2).

The space between the first plate (1) and its shield plate (11), or thespace between the second plate (2) and its shield plate (11), forms achamber protecting the welds between the exchange tubes (3) and the mainplates (1, 2).

The shield plates (11) have perforations to allow the passage of theexchange tubes (3). The perforations of the shield plates (11) allow thepassage therethrough, but the shield plates (11) are not necessarilyattached to the exchange tubes (3). As they are not attached to theexchange tubes (3), there is no damage to the welds, nor are theyaffected by the expansion of the exchange tubes (3).

FIG. 5 shows the second walls (7), independent of the shield plates(11). According to another embodiment, both are configured from one andthe same plate.

According to another embodiment, the second internal walls (7) areprolonged inside the intake manifold (8) of the second fluid, inside theexhaust manifold (9) of the second fluid, or inside both. Thisprolongation is spaced from the corresponding manifold (8, 9) forming achamber offering protection from direct contact with the hot gas.

FIG. 6 shows an embodiment of a side wall (6, 7), with the prolongationsfor the manifolds (8, 9). The use of two symmetrical parts as shown,facing one another, establishes the walls on both sides of theevaporator, as well as the chambers for protecting the manifolds (8, 9).This side wall (6, 7) shows a corrugation that is prolonged along thelongitudinal direction X-X′ so that the side wall (6, 7) is elasticallydeformable at least in the direction joining the first plate (1) and thesecond plate (2).

The configuration of the first inner-walls (6) and of the second innerwalls (7) can differ in dimensions of the parts thereof so that thewalls (6) and other walls (7) can be arranged parallel, can maintain thesurfaces inside the intake manifold (8) and exhaust manifold (9) forminginner chambers in both cases, and it can also differ in the corrugationor crimps (6.1, 7.1) providing the elastically deformable behavior todetermine the degree of stiffness thereof.

Once the two parts are attached as shown in FIG. 6, the upper edge isconfigured for being adapted to the periphery of the first plate (1) andthe lower edge is configured for being adapted to the periphery of thesecond plate (2).

Therefore, each of the parts shows a U-shaped configuration where thearms of the U are the prolongations housed inside the manifolds (8, 9)of the second fluid. Once they are attached to one another, they giverise to the walls (6, 7) of the evaporator.

At the beginning of the description it was indicated that expansion ofthe exchange tubes (3) is greater at one end of the evaporator than atthe other end. In the general case, given that the three steps areidentified in the evaporator, the increase in temperature is not linear,nor is the degree of expansion of the exchange tubes (3) according tothe longitudinal direction X-X′ according to the forward movementdirection of the flow of the second fluid.

According to another embodiment, the first plate (1), the second plate(2) or both (1, 2) are elastically deformable, allowing bendingaccording to an axis parallel to such plates and perpendicular tolongitudinal direction X-X′.

The property of being elastically deformable according to thisdirection, according to the described embodiments, is achieved byconfiguring the chambers (1.1, 2.1) of the plates according to thetransverse direction with respect to the larger sides of the plate (1,2) and by choosing the means for closing the chambers on the outer face,facilitating said elastic deformation.

1. An evaporator for the evaporation of a first fluid by means of theheat provided by a second fluid, the second fluid being a hot gas,wherein said evaporator comprises: a first plate (1) and a second plate(2) facing one another and arranged spaced from one another, defining aninner face, the face facing the other plate, and an outer face oppositethe inner face; wherein each of the plates (1, 2) comprises a pluralityof chambers (1.1, 2.1); an intake manifold (4) of the first fluid and anexhaust manifold (5) of the first fluid situated in fluid communicationwith one another and with at least one different chamber (1.1, 2.1) ofany of the plates (1, 2); a plurality of heat exchange tubes (3) whereineach of the heat exchange tubes (3) extends between a chamber (1.1) ofthe first plate (1) and a chamber (2.1) of the second plate (2); whereineach chamber (1.1, 2.1) of one plate (1, 2) is in fluid communicationwith two or more chambers (1.1, 2.1) of the other plate (1, 2) by meansof at least two heat exchange tubes (3), except the chambers (1.1, 2.1)in fluid communication with the intake manifold (4) or the exhaustmanifold (5); there being for each of the heat exchange tubes (3) a pathof fluid communication from the intake manifold (4) to the exhaustmanifold (5) passing through the inside of said heat exchange tube (3);two first side walls (6) extending between the first plate (1) and thesecond plate (2) housing the plurality of heat exchange tubes (3) andestablishing between both a space for the passage of the second fluid,wherein the second fluid enters through an inlet (I2) and exits throughan outlet (O2); characterized in that the first side walls (6) areelastically deformable, which allows compensating the differentialexpansion between the heat exchange tubes (3) and said first side walls(6).
 2. The evaporator according to claim 1, wherein the tubes (3) areelastically deformable according to their longitudinal direction.
 3. Theevaporator according to claim 1, wherein said evaporator additionallycomprises second side walls (7), situated between the first plate (1)and the second plate (2), these second side walls (7) being spaced fromthe first side walls (6), wherein the second side walls (7) areelastically deformable and are arranged internally with respect to thefirst side walls (6).
 4. The evaporator according to claim 3, whereinthe first side walls (6), the second side walls (7), or both, areelastically deformable by means of one or more crimps or corrugations(6.1, 7.1).
 5. The evaporator according to claim 4, wherein the crimps(6.1, 7.1) have a main direction according to the longitudinal directionestablished between the inlet (I2) and the outlet (O2) of the secondfluid.
 6. The evaporator according to claim 4, wherein the crimps (6.1,7.1) have a sinusoidal path.
 7. The evaporator according to claim 3,wherein the stiffness constant of the elastically deformable second sidewalls (7) is less than the stiffness constant of the elasticallydeformable first side walls (6).
 8. The evaporator according to claim 1,wherein the inlet (I2), the outlet (O2), or both, have a manifold (8,9).
 9. The evaporator according to claim 3, wherein: a. the second sidewalls (7) are prolonged inside one or more intake/exhaust manifolds ofthe second fluid (8, 9); and, b. at least one prolongation of the secondside walls (7) inside the manifold (8, 9) is spaced from said manifold(8, 9).
 10. The evaporator according to claim 3, wherein between thefirst side walls (6) and the second side walls (7) there is a chamberthat is in fluid communication with the intake manifold (4) of the firstfluid such that the entrance of the first fluid in the evaporator iscarried out by means of previous passage through the chamber formedbetween the first and second side walls (6, 7).
 11. The evaporatoraccording to claim 1, comprising: either a first shield plate (11)located in the passage space of the second fluid, spaced from the firstplate (1), or a second shield plate (11) located in the passage space ofthe second fluid, spaced from the second plate (2); or, or both thefirst and second shield plates (11); wherein the shield plates (11) havemultiple of perforations for the passage of the heat exchange tubes (3)leaving a chamber between said shield plates (11) and theircorresponding plates (1, 2) for protecting the welds between theexchange tubes (3) and said plates (1, 2).
 12. The evaporator accordingto claim 3, wherein the second side walls (7) and the shield plate orplates (11) are configured as a single part.
 13. The evaporatoraccording to claim 3, wherein there are thermal insulation means in thechamber (10) situated between the first side walls (6) and the secondside walls (7).
 14. The evaporator according to claim 3, wherein eitherthe first side walls (6), the second side walls (7), or both (6, 7),extend along the outer side of the first plate (1) and along the outerside of the second plate (2), being attached to one another, configuringa shell.
 15. The evaporator according to claim 14, wherein either thefirst side walls (6), the second side walls (7) or both, are configuredin the form of two U-shaped halves attached to one another.
 16. Theevaporator according to claim 1, wherein the first plate (1), the secondplate (2), or both (1, 2), allow bending according to the directionperpendicular to the longitudinal direction established between theinlet (I2) and the outlet (O2) of the second fluid.
 17. A heat recoverysystem for internal combustion vehicles comprising an evaporatoraccording to claim 1.